Conventionally, Patent Literature (PTL) 1 describes a power supply device in which a plurality of battery packs is respectively housed in housing spaces partitioned and formed in a rack. Each of the battery packs is constructed by combining a plurality of single cells. In this power storage device, when the battery packs are inserted and housed into housing spaces, respectively, output terminals disposed to rear surfaces of the battery packs are inserted into input terminals installed in the back of the housing spaces. Thus, the plurality of battery packs housed in the rack is connected to each other in series or in parallel at a rear surface side of the rack by connection leads connected between the input terminals.